Computer memory is a relatively fast storage medium in the sense that data stored in computer memory can be accessed quickly. The amount of memory that a CPU can directly access is limited by the CPU address space. A computer system's performance is dependent upon the size of the address space and the amount of memory available. System performance can be improved by using large amounts of memory as a storage medium rather than a disk, which is a relative slow storage medium. System performance can also be improved by increasing the effective address space of the CPU.
Computer systems typically use disk drives to store large amounts of data permanently. A computer system must transfer the disk data from the disk into the computer memory before the CPU can access the disk data. The transfer of data from disk to computer memory is a relatively slow process compared to the transfer of data from one computer memory location to another. When a computer program frequently requests disk data, the CPU may spend significant amounts of time waiting for the data to be transferred from the disk to memory so that it can process the data.
Computer systems often use a technique known as disk caching to improve system performance and minimize this waiting time. In disk caching large blocks of disk data are loaded into memory at one time. When a program actually needs the disk data, then it is copied from memory locations in the disk cache to memory locations within the program
The computer's operating system typically manages the disk caching process This relieves the application program from the burden of such management.
System performance is affected by the amount of storage allocated to disk caching. Generally, a large disk cache results in better system performance.